1. Choose a number with repeating 9's and a final 6.
2. The square is made up of:
   • same number of 9's as there are repeating 9's
   • a 2
   • one fewer 0 than repeating 9's
   • a final 16

   Example:

1. If the number to be squared is 9996:
2. The square has:

   same number of 9's
   as repeating 9's:    9 9 9
a 2                           2
one fewer 0 than there
   are 9's in the square        0 0
a final 16                          1 6

3. So 9996 × 9996 = 99920016.

   See the pattern?

1. If the number to be squared is 999996:
2. The square has:

   same number of 9's
   as repeating 9's: 9 9 9 9 9
a 2                            2
one fewer 0 than there
   are 9's in the square         0 0 0 0
a final 16                               1 6

3. So 999996 × 999996 = 999992000016.